This invention relates to the float process for forming flat glass where molten glass is continuously delivered onto one end of a pool of molten metal, where it is drawn to a ribbon of desired thickness and withdrawn as a continuous ribbon of glass from the opposite end of the pool of molten metal. More particularly, this invention relates to improvements in the delivery section of such an apparatus. In the delivery section, the flow of molten glass from a melting furnace into the forming chamber is regulated by means of one or more vertically adjustable gates known as "tweels." A tweel typically comprises a ceramic piece in contact with the molten glass and supported from above on a steel bridge structure, which is external to the molten glass containing enclosure. Typically, floor mounted jack screws engage the bridge structure and adjust the height of the tweel. An example of such an arrangement may be seen in U.S. Pat. No. 3,764,285 (Matesa et al.).
Because the lower tip of a tweel is in constant contact with molten glass moving at a relatively high velocity, a tweel is subject to erosion and, therefore, usually must be replaced at intervals considerably shorter than a normal furnace campaign. To replace a tweel, an overhead crane is usually employed to lift the tweel and bridge structure above the delivery section of the furnace so that the tweel may be disassembled from its supporting structure and a new tweel installed in place thereof. Providing a crane in that region of the installation is costly due to the high temperature environment. Working on the tweel above the delivery section of the furnace is also inconvenient.
The final piece of refractory over which the molten glass flows before flowing onto the molten metal support in the forming chamber is termed the "threshold" (or "lipstone"). Because a threshold is also subject to heavy wear and must occasionally be replaced, it is considered desirable to mount a threshold on movable support means to enable the threshold to be extracted laterally from the delivery section. However, the floor mounted jack screws employed in the prior art for adjusting the height of the tweel obstruct the lateral retraction of a threshold. Therefore, it would be desirable for tweel height adjustment to be provided in a manner that does not interfere with lateral threshold movement.